What Could Possibly Go Wrong?
by GraceWinter
Summary: In the 21st century a cure has been found for 'yin fen', so Jem has left the Silent Brothers. However, he is left with the effect of immortality. To celebrate, Magnus takes Jem and Tessa on a journey around the world - no demons, no fighting, just a peaceful holiday. But with their complicated pasts (and Magnus's dress sense!), is 'normal' even a possibility? A Jessa/Malec story.
1. Chapter 1

Chapter One

Tessa still couldn't get used to the clothes of this century. _Denim trousers?_ she thought, forgetting the name for them. _Has it really come to this?_ She much preferred the dresses she had worn as a teenager, when she first met the Shadowhunters... Tessa shook her head. She needed to stop grieving - it had been decades since Will passed away.

Despite the rising sun everything in Central Park was sheathed in a layer of frost. Shivering, Tessa huddled into her hoodie - another garment she couldn't get used to. She stared idly at the birds darting through the trees. As she sat uncomfortably on the park bench, she saw a figure coming through the morning mist.

Squinting, she tried to recognise the figure. Jem was due to meet her here, but he was late. Him being a Silent Brother, meetings with him were rare. Had he forgotten? No, Jem wouldn't forget.

As the figure drew closer, Tessa saw the figure wore jeans and a t-shirt; not the robes and runes of a Silent Brother. His hair was dark, like Jem's, but not streaked with silver. He didn't use a cane to walk, as Jem did. But the face seemed so familiar...

" _Jem?_ " Tessa stood up, hardly believing her eyes.

"Yes, I know. Tessa, let me explain..."

Jem sat down next to Tessa. He no longer had the rigid movements of a Silent Brother - this was the Jem he had been all those years ago, the young man she had missed so much.

"They found a cure to the drug." Jem's dark eyes sparkled with excitement.

"So... You're not a Silent Brother anymore? Are you still a Shadowhunter? Are you mortal now?" Tessa's questions came all at once, the shock overwhelming her.

"Ah, that's the difficult part."

"What do you mean?"

"Well, I don't need to be a Silent Brother. As for the other thing..." Jem hesitated. "The Brothers told me that even though I will no longer be one of them, I will be left with the effect of immortality. So I can never have a normal life."

Tessa bit her lip, pondering the situation. Was Jem's immortality good news? Neither of them knew, but Jem realised he'd need somewhere to stay.

"Well, my apartment's too small, but don't worry - I know just the place."


	2. Chapter 2

Chapter Two

"Tessa! It's been too long! Oh, and... James Carstairs? Weren't you a Silent Brother?"

Magnus Bane answered the door with enthusiasm and a flourish of his rather extravagant hat.

"It's a long story. We're both tired, and we were wondering... is there room for us to stay here? Just until Jem gets used to the 21st century!" Tessa laughed delicately, but her eyes betrayed the anxiety she felt.

"Of course there's room - my voice practically echos in this place! We'd be delighted to have visitors."

A rather bemused Alec came towards them from the kitchen. He looked at Magnus for an explanation.

"Alec! There you are. These people will be staying with us for a while. Of course, you know about Tessa. Tessa, James -"

"Er, you can call me Jem."

"Yes. Tessa, Jem, this is Alexander, my... close friend."

Tessa and Jem managed to figure out what he meant - after all, they knew Magnus. They also knew his fashion sense - flamboyant at the best of times, disastrous at the worst - so they didn't question the outfit that he wore.

Earlier that day Alec had audibly sighed when he saw Magnus's chosen outfit, but Magnus saw nothing wrong with it; green silk trousers and a gold sequinned waistcoat were perfectly fashionable items in his opinion. Dull, really, compared to the peacock-feather hat he'd once worn when visiting a certain blonde-haired vampire. Or his blood-red velvet jacket, trimmed with gold brocade, which had been her particular favourite... _Drat._ He had to stop thinking about Camille.

Magnus was abruptly broken out of his reverie by Alec.

"I guess we should show Tessa and Jem to their rooms?" prompted Alec. He rolled his eyes at Magnus's startled expression. Alec rolled his eyes rather too frequently, Magnus thought.

"Yes, yes! Of course!" Magnus's eyes seemed too bright, his voice artificially cheerful. Alec wondered what he had been daydreaming about. "You can spend some time getting accustomed, but an event like this deserves a celebration."

Tessa and Jem exchanged a nervous glance, wondering what was in store. Magnus's celebrations verged on opened her mouth to ask what exactly he had in mind, but Magnus held up a hand to silence her.

"No questions - I believe surprises are good for the mind and soul! But as a young Welsh man once told me," - Magnus winked at them both - " _Fe hoffwn i fod mor feddw, fyddai ddim yn cofio fy enw._ "


	3. Chapter 3

Chapter Three

Magnus was true to his word. He matched his gold waistcoat with a pair of sequinned ankle boots – much to Alec's exasperation – and led his guests out of the apartment. After a few minutes of walking and several funny looks from strangers, they all piled into a small yellow cab.

"Where to?" inquired the driver, trying not to stare at the strange party in the back of his cab.

"We're in for a night of dancing and strangely-coloured cocktails – I think you can guess where!" Magnus laughed.

Alec could only imagine what the driver was thinking. He liked Magnus a lot – maybe even loved him, though it was a bit too soon to say – yet he seemed intent on going again all conventionality. His clothes, his actions, and his _debauchery_ in Peru… no wonder Robert and Maryse didn't approve. Magnus's immortality also caused Alec to be jealous - when he was gone, he knew Magnus would find someone else. The thought was unbearable.

The recent war with Valentine and his demon army had made Alec realise just how fleeting life really was. Some Shadowhunters thought they were so much better than mundanes, but Alec knew that when it came to lifespan they were all equal. While warlocks and vampires passed effortlessly through time, everyone else would die.

"Are you okay?" Magnus asked softly. "You look… distracted."

"I'm fine."

The group sat in silence for the rest of the journey.

Ten minutes later, the cab parked up outside the Pandemonium Nightclub.

"Oh, God. It's finally happened." Alec declared as they stood on the sidewalk. "Magnus, you've gone insane."

Magnus blinked. "I think that happened a long time ago, Alexander."

Jem smiled and nodded in agreement, while Tessa giggled quietly. Alec's face was the living embodiment of an approaching storm.

"MAGNUS. We need to talk."

Alec _hated_ the Pandemonium. It was often haunted by Eidolon demons – sometimes there of their own accord, sometimes sent by scheming warlocks, always part of some nefarious plot. The dance floor was occupied by stupid mundanes attracted by the strange rune-like symbols on the neon sign. Even worse than that: it was where he, Jace and Izabelle had first met Clary.

He no longer disliked Clary. She made Jace happy; everyone could see how much he'd changed since he met her. But Alec couldn't help thinking that maybe if Clary, Valentine's daughter, hadn't got involved in the Shadow World… Maybe the war with Valentine wouldn't have happened. Maybe, just maybe, Max would still be alive.

He stormed off, Magnus scurrying after him.


	4. Chapter 4

Chapter Four

Jem was glad to be out of the Silent City, but he was rather taken aback by… well, by all of _this._ He'd been forced to borrow clothes from Magnus, having only brought one outfit. After Jem had selected the plainest and least sparkly items, Magnus had announced that he looked 'fabulous'. Jem wasn't exactly thrilled by this comment. Marvelling at the flashing neon signs and loud dance music, he tried – and failed – to ignore the argument going on a few metres away.

"Magnus, you _know_ how I feel about this place."

"Sometimes we have to let go of bad memories, Alec. It's the only way to be happy."

"I... I don't know what you're talking about. What I meant was that this place is quite popular with demons."

"You're not kidding anyone. Look, we won't be there for long, we're just showing Jem and Tessa what the modern world is like. Please? Pretty please?"

Alec paused, looking into Magnus's green catlike eyes. "Fine! But _never_ say 'pretty please' again."

As they entered the nightclub, Jem felt dizzy. Bright lights and fast-moving figures swam before his eyes. The music seemed louder than anything he'd ever heard. Until Tessa took his hand.

"This is the first time I've been in a nightclub, too." confessed Tessa, worry flickering in her eyes. I'm sorry if taking your hand seems rather forward; I'm really quite scared."

Jem smiled wistfully. "Tessa, you forget - we were engaged, once upon a time."

Tessa blushed and looked away. Jem stood still for just a moment, mildly shocked at what had passed between them - but a moment was all it took. He was separated from Magnus and the others.

Eyes darting through the crowd, Jem searched for his friends, but it was no use. The nightclub was too large, too crowded, too overwhelming. Jem resigned himself to watching the people around him, and wasn't surprised to see a few Downworlders. They were glamoured, of course, but lightly. Jem's Sight allowed him to easily see through these glamours, like lifting away a layer of gauze. His eyes settled on a young woman near to him; her hair was scarlet - dyed? - and her eyes were dark as an abyss. There was a glamour on her, but heavier than the others - like a curtain of velvet rather than gauze. Squinting, Jem managed to lift a glamour and see what the woman really was.

A demon.

 _Nephilim,_ it hissed seductively. _Come here, angel boy._

"Who do you think I am - Benedict Lightwood?" replied Jem scornfully. He saw the shock on the demon woman's face. "Yes, I thought you might remember him. I know your game."

The demon's manner abruptly changed. _I despise you, Nephilim brat._ It spat out the words. _I shall rip you to shreds and drag you to the fires of Hell._ It began to walk towards him. Jem had no weapons, no stele, nothing to protect him.

"How delightful." Magnus had appeared behind Jem, with Tessa and an irritated-looking Alec. "James - RUN!"


	5. Chapter 5

Chapter Five

Tessa was having a wonderful evening. The glass in her hand was filled with sparkling green liquid; when she drank from it she felt a tingling warmth spreading through her body. Clutching her drink, she stood and stared with fascination at the other partygoers. The majority of them were dancing, or at least swaying drunkenly, on the dancefloor; some were at the bar, drinking similar beverages to hers; Magnus was talking animatedly with a group of Downworlders, and Alec was sulking. So, yes, she was having a wonderful time – that is, until she realised she'd lost sight of Jem.

Just as Tessa started looking for him, Jem came running towards her, leaving a crowd of irritated people in his wake. He looked unusually flustered. _Oh, Jem, what have you got yourself into?_ thought Tessa, sighing heavily.

"Over there... the girl with the red hair... she's a demon!" gasped Jem as he jolted to a halt, almost colliding with Magnus. "I've got no weapons. We need to get the mundanes out of this place."

Magnus responded calmly and sensibly to the impending danger - battle was probably the only time he behaved sensibly. "Tessa, Jem, in a moment I'm going to set off the fire alarm; that will get the mundanes out. When I do that, you have to leave too. Do you understand?"

"We're Shadowhunters, Magnus. Let us stay here." replied Tessa determinedly.

"Well, I suppose..."

" _No._ " Alec surprised everyone; he had hardly spoken since they'd left the cab. "They only know the basics of magic, and neither of them have any weapons. They can't stay, Magnus."

"That's a good point, actually. Besides, I don't want you dropping dead on your first night out."

Tessa began to argue, but Jem gently put his hand on her shoulder, silencing her. Blue sparks flew from Magnus's fingertips, the fire alarm began to shriek, and Jem and Tessa ran to the fire exit.

 **Only a short chapter, I've been really busy today but I will write a longer chapter tomorrow! Thanks for reading :)**


	6. Note

**Note:**

 **Sorry for not updating this story, I've been really busy this week so I haven't been able to write much. I'll try to write this weekend. Thanks for reading!**


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